A gas laser corresponding basically to the description hereinbefore given has been described in European Patent No. EP-B-O-048 690. The discharge tube includes metallic bodies having high thermal conductivity, for instance of aluminum alloy generally taking the form of discs provided with cooling fins and having an opening pierced in their center. These metallic bodies are arranged end to end so that their central openings are aligned and form the laser discharge tube. Such tube is intended to be filled with a gas, for instance argon, under slight pressure.
End chambers one of which includes a cathode and the other an anode are arranged respectively at each end of the tube. Such anode and cathode are intended to create and maintain an electrical discharge in the gas filling the tube.
The metallic bodies of the tube are fixed to an envelope exterior to the latter in a manner to compress them against one another and thus to compress the toroidal seals located between these bodies and formed of rubber or other plastic material.
During operation of the laser, the several metallic bodies of the tube are brought to different potentials and the wall of the tube is subjected to an intense ionic bombardment from the plasma formed by the gas filling the tube. The bodies forming the tube must thus be protected against erosion produced by such ionic bombardment and to be electrically insulated from one another. This protection and insulation are assured by means of an insulating layer preferably of aluminum oxide which covers entirely the metallic bodies.
The heat given off by the electrical discharge maintained within the gas filling the tube during operation of the laser is removed by a fluid which may be water circulating in the space situated between the fins of the elements and the outer element of the tube.
The gas discharge tube described hereinabove exhibits certain disadvantages.
Thus, the increase in the temperature of the metallic bodies of the tube during operation of the laser brings about expansion of these elements. Since the expansion coefficient of the material of the metallic bodies is different from that of the insulating layer which covers them, such expansion causes cracks to appear in the insulating layer. The presence of such cracks permits the cooling liquid of the tube to penetrate to the interior of the latter which prevents proper operation of the laser.
In addition, when the laser is put into service or following a prolonged interruption of its operation, the tube must be evacuated of the air or gas contained therein before being filled or refilled by the desired gas. As is well known, this evacuation is facilitated and improved by simultaneous heating of the tube.
However, the presence of rubber or plastic material seals between the metallic bodies prevents heating the tube to a temperature as high as would be desirable. Furthermore, the seals retain at their surface a non-negligible quantity of air or gas, the presence of which increases notably the duration of this evacuation operation.
In the same manner, such seals may be destroyed by the ionic bombardment originating from the plasma formed in the tube during operation of the laser. The metallic bodies of the tube must thus be provided with ribs and grooves disposed so as to protect the seals against such bombardment. Such ribs and grooves complicate the manufacture of these elements and increase their cost.
In order to avoid these difficulties, it would be possible to replace the seals of plastic material by metallic seals, for instance of copper or aluminum, such as those which are currently employed in apparatus including a sealed enclosure which must withstand high differences in pressure and/or temperature.
The employment of such seals enables heating the tube to a high temperature during the evacuation of the cavity. In addition, such seals permit resolving the sealing problem caused by the appearance of cracks in the insulating layer covering the elements of the tube. Effectively, the metal of these seals is sufficiently soft so that it may penetrate into these cracks and block them completely when the seals are forcibly compressed between two elements of the tube.
Finally, these metallic seals are less sensitive to ionic bombardment from the plasma during operation of the laser.
However, when such metallic seals are compressed between two metallic bodies of the tube so that they penetrate into the cracks of the insulation layer of these elements, they may come into contact with non-protected metal at the bottom of such cracks and thus provoke a short-circuit between such elements, this preventing operation of the laser.
On the other hand, compressing means such as those which have been described in the Patent No. EP-B-O 048 690 mentioned hereinabove must be dimensioned so as to exert on the tube the sum of the forces which must be applied to each one of the seals in order that the latter assure sealing of the tube. Each of these forces is much greater when the seal is metallic rather than when it is of plastic.
If the seals are metallic and if the number of elements of the tube is relatively great, the total force which must be exerted by the compression means becomes very substantial. In such a case, compressing means such as those which have been described in the Patent No. EP-B-O 048 690 are unusable in practice since their dimensions become much too great.
To overcome this difficulty one could provide, rather than a single compressing means, as many compressing means as there are metallic bodies forming the tube, e.g. screws pressing two of these bodies against one another alternatively.
Whatever may be the solution chosen, that of the cited patent or that which has just been suggested to remedy the difficulties thereof, there will always be the necessity of providing compressing means for the assembly of the tube and such means will require parts particularly adapted to this end and necessitating an assembly time which may be substantial. The systems so far proposed moreover are inadequate to guarantee absolute sealing. At the limit they may be admitted for a laser the interior of which is accessible since, in such case, defects of sealing or of insulation of one of the metallic bodies may be overcome or remedied by disassembling the tube and changing the defective body. A sealed laser on the other hand must exhibit during its entire life an absolute sealing and perfect insulation between the elements since in principle it is not repairable in view of the inaccessibility of its interior. Such lasers are often preferred to dismountable lasers because of their greater reliability.
The principal object of this invention is to provide a gas laser in which the anode and cathode chambers and the metallic bodies of which the discharge tube is comprised are hermetically sealed to one another while being insulated from one another.
Another purpose of the invention is to provide a gas laser which is completely sealed and comprises, in addition to the anode and cathode chambers and the discharge tube already mentioned, anode and cathode supports sealed to the anode and cathode chambers, said supports bearing in a sealed manner the Brewster windows, the electrode passages and the pumping channels.
A further purpose of the invention is to provide a method of assembling of the internal parts of such gas laser including the anode and cathode chambers and the discharge tube.